/Engine/Source/Runtime/Engine/Public/GPUSkinVertexFactory.h
The bucket sizes
static uint32 BucketSizes = { 16, 48, 96, 192, 384, 768, 1536, 3072, 4608, 6144, 7680, 9216, 12288, 65536, 131072, 262144, 786432, 1572864 };